Hi. I just got a service engine soon light so I checked the code and it came back as code 172 which is bank 1 rich. I was going to give it a try to fix it since I enjoy working on cars before I take it in. I don't think it is a bad 02 sensor since the car has less than 50k miles. It's running rich so I think it might be a leak in a vacuum line. What else could it be? The car is a 2009 135i. Thanks for any help in advanced!